1. Field of the Invention:
The present invention relates to a composition of matter which comprises an iron oxide of spinel structure, also containing trivalent and monovalent metals forming part of the spinel structure, and to the use of such composition as a catalyst for dehydrogenation, particularly of ethylbenzene to styrene.
This invention also relates to the preparation of such composition of matter by the decomposition of a mixed organic iron salt of said trivalent and monovalent metals, followed by a reduction in the presence of hydrogen and steam and, if appropriate, an oxidation.
2. Description of the Prior Art:
The dehydrogenation of hydrocarbons is a reaction which quite frequently is carried out on an industrial scale, for example to prepare butadiene from butene or styrene from ethylbenzene. Patent FR 2,506,294 describes a dehydrogenation catalyst consisting of iron oxide of spinel structure containing trivalent metals such as aluminum and chromium, and divalent metals such as calcium and manganese, all such metals being in the spinel structure. The spinel structure also contains lithium and may contain sodium, silver or copper. This catalyst is improved by the addition of alkali metal oxides and of vanadium oxide outside the spinel structure. The surface of a catalyst of this type does not exceed 2 m.sup.2 /g.
European Patent Application No. EP 177,832 describes dehydrogenation catalysts formed by calcining oxides of iron, chromium, potassium and magnesium.
A low surface catalyst is often relatively inactive, that is to say, a large amount of it is necessary to ensure a given hourly production of dehydrogenated product, and metal oxides which do not form part of the spinel structure tend to migrate out of the catalyst and disappear.